The invention relates to water hydrants of the type for extending through an outside wall of a building and having an external hand wheel or the like for turning a valve stem to reciprocate within an elongated passage. At the inner end, the passage is connected to a source of water under pressure and a water shut-off valve at the inner end of the stem, remote from the wall, engages a seat when the valve is closed. The outer end of the hydrant is typically externally threaded for attachment of a water hose.
It has been recognized that water can become trapped within the hydrant after closing of the valve. If the water freezes, as can often occur in colder climes, the hydrant can be damaged, resulting in costly repairs or replacement. There has also been recognized a danger of backflow of chemicals or other contaminants from the hose into the potable water supply, e.g. as result of back-siphonage due to loss of system pressure.
In order to protect against both of these conditions, it has been suggested, e.g. by Pike et al. U.S. Pat. No. 4,475,570, the disclosure of which is incorporated herein by reference, to include an outlet spout valving arrangement that admits air into the hydrant after each closing to release trapped water and thus avoid damage by freezing, and also that resists backflow from the outlet into the hydrant.
According to the existing standard of the American Society of Sanitation Engineers (ASSE Standard 1019), the hydrant must drain when the shut-off valve is closed, without regard for whether or not a hose is attached at the outlet. It is recognized that a hydrant constructed to meet this standard can have an increased possibility for contaminating backflow if the hose remains in place. An alternative standard proposed for consideration would require that the outlet spout valving arrangement actuate to drain the hydrant only if there is no hose attached at the outlet. This standard is intended to lessen the possibility of system contamination, but a hydrant constructed to this standard would also be more susceptible to damage due to freezing of entrapped water when the hose is left in place.